Nutrition and growth of rainbow trout (Oncorhynchus mykiss) fed diets supplemented with a synbiotic preparation

doi:10.21203/rs.3.rs-2475472/v1

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Nutrition and growth of rainbow trout (Oncorhynchus mykiss) fed diets supplemented with a synbiotic preparation

https://doi.org/10.21203/rs.3.rs-2475472/v1

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This study was carried out in order to assess the effect of inulin and Bacillus on nutrition and growth indices of rainbow trout (Oncorhynchus mykiss). For this purpose, 525 of fish rainbow trout with an average weight of 56.84g ± 4.32 were purchased from fish breeding farm and transferred to the aquaculture department of Shiraz University. After initial adaptation and one week of quarantine, 25 fish were stored in each 500 L polyethylene tank. The duration of the experiment was 60 days. Triplicates were used for each treatment experimental groups included a control (C) without any supplement, treatment (A) with a level of 0.5% inulin, treatment (B) with a level of 1.5% inulin, treatment (D) with a concentration of 10³ CFU/g Bacillus, treatment (E) with 10⁶ CFU/g Bacillus, treatment (F) with 10³ CFU/g Bacillus and 0.5% inulin and treatment (H) with 10⁶ CFU/g Bacillus and 1.5% inulin. The ratio of feed conversion on 15th, 30th and 60th days in F treatment showed a significant increase compared to other treatments, but on 45th day, the highest rate of this index was observed in treatment H. At the end of the experimental period, treatment D had the highest percentage of specific growth rate with a significant difference compared with other treatments. The highest level of protein efficiency coefficient was observed on 15th, 30th and 60th day of the experiments for the group F and on 45th day in the group containing 10³ CFU/g Bacillus. The highest level of fat efficiency ratio was observed in the mentioned days in F treatment. On 45th and 60th day of the experiment, the fat efficiency ratio in treatment D was higher than other treatments. It can be concluded that the simultaneous use of Bacillus and inulin can have the highest positive effects in rainbow trout growth.

Rainbow trout (Oncorhynchus mykiss)

Inulin

Bacillus

Synbiotic

Growth and nutritional indices

The synbiotics were loosely defined as mixtures of probiotics and prebiotics that beneficially affect the fish host. A general misunderstanding might have been, in part, because the original definition itself — that is, “mixtures of probiotics and prebiotics that beneficially affect the host by improving the survival and implantation of live microbial dietary supplements in the gastrointestinal tract, by selectively stimulating the growth and/or by activating the metabolism of one or a limited number of health-promoting bacteria, thus improving host welfare” — was too wordy and lacked precision [39].

The use of probiotics in aquaculture is now widely accepted but very few studies have focused on the effects of probiotics in aquaculture. The consensus from these research studies is that both pro-and prebiotics positively effects on growth of rainbow trout. Research on the effects of probiotics upon growth performance of fish especially in rainbow trout is very scarce [24]. Thus, there is clearly a need to increase our knowledge of the effective preparation and safety evaluation of probiotic. The B. subtilis, one of the most studied probiotics in fish, is able to grow at a vast range of temperatures (10–50°C), pH values, and NaCl levels (0% − 9%) suggesting that it can be used for various purposes in aquaculture, such as probiotics for all fish species, immunostimulation and disease resistance [16]. Rainbow trout (Oncorhynchus mykiss) is a high production species for aquaculture in many countries [5]. It is widely cultured in Iran. However, intensification of culture systems leads to stress and causes diseases in trout farming, which accounts for a significant decrease in production levels in local farms [9, 18, 22, 27].

Inulin is a group of natural polysaccharides that can be used to feed fish. It also contains fiber, which is not digested by digestive enzymes in the gastrointestinal tract, but has a unique function in the intestine and increases the intestinal flora, such as lactic acid bacteria, and has beneficial effects on the modulatory system of the immune system [33].

Probiotics have attracted extensive attention in aquaculture [26], as non-digestible feed additives that metabolizable through gut microbiota [25]. They provide a beneficial influence on the fish health through selective growth inducement, metabolizing health-inducing bacteria in the intestinal tract, and/or improving the host’s intestinal balance [14, 19]. The previous studies on inulin have been focused on the improvement of growth performance and general health conditions [28]. The aim of this study was to investigate the effect of synbiotic of inulin and Bacillus on growth and nutritional parameters of rainbow trout.

The present research was conducted at 2021 in the aquaculture department of Shiraz University, Iran. The experiment was designed in a completely randomized design including zero (control), different levels of 0.5%, 1% and 1.5% w with our treatments and triplicate. The 525 fish with an average weight of 56.84g ± 4.32 (SD) g were purchased from the fish farm in Fars province and transferred to the aquaculture department of the university with basic aeration. First, the fish were disinfected with 250 ppm formalin for 60 min. After a week of adaptation to the new environmental conditions, 25 of fish were stored in each 500 L dehydrated polyethylene tank. The duration of the experiment was 60 days. Each treatment was conducted in triplicate. During the experiment, water parameters such as temperature, dissolved oxygen, pH and salinity were measured regularly. 20% of the water volume of the tanks was changed daily. Tanks then were aerated. Temperature during rearing period was 14.21 ± 2.6°C, dissolved oxygen content was 5.87 ± 1.3 and pH was 7.6 ± 0.13. The inulin and Bacillus were used in this study.

Preparation of experimental treatments

The experimental diets were, treatment (A): 0.5% inulin, treatment (B): 1.5% inulin, treatment (D): a concentration of 10³ CFU/g Bacillus, treatment (E): a concentration of 10⁶ CFU/g Bacillus, treatment (F): a concentration of 10³ CFU/g Bacillus and 0.5% inulin and treatment (H): a concentration of 10⁶ CFU/g Bacillus and 1.5% inulin insulin which added to the basic diets. The control group was (C): without adding any supplements.

Bacillus used in this research was obtained from Ariana Biotechnology Complementary Development Company. This microbial product contains three types of Bacillus Licheniformis, Bacillus subtillus and Bacillus filamentosus, which has a population of 10⁹ CFU/g. The inulin used in this research was inulin (Raftilin ST) with a degree of polymerization of 2–60%, which was obtained from ORAFTI Company, Belgium.

Preparation of fish feed

The extruded feed was prepared from Beyza 21 factory located in Fars province, Iran.

Chemical composition of the fish feed was shown in below:

The proximate analysis of the fish feed used in terms of percentage was as follows: moisture 12%, crude protein 43–46%, crude fat 11–15%, crude fiber 1.5-3% and digestible energy was 4300 calories.

In order to supplement additives in the diets, the feed was first soaked in sterile water and then made to a paste, and then dietary supplements containing probiotic added to the feed in the correspondent dilution. Afterwards, the mixture was mixed and homogenized. Then the feed dried using a meat grinder in the shape of a pellet of appropriate size with the fish's mouth [31]. The fish feeding was carried out in triplicate a day which was equal to two percent of fish body weight. To minimize bacterial spoilage in the prepared diet, feed was prepared daily and the fish was fed. The amount of daily feed was calculated weekly and based on new biomass for each tank separately.

Fish biomass ×% feeding = total daily feed intake

Fish biomass was obtained by multiplying the number of fish by the average weight of the fish.

Fish bioassay with random sampling of 10 fish for each group was performed at the beginning of the period (day zero) and then every two weeks until the end of the period with the aim of assessing the growth rate of the fish. For this purpose, growth factors and nutritional indicators such as total length, percentage of weight gain (G.R.), specific growth rate (S.G.R), feed conversion ratio (F.C.R.) and feed efficiency (F.E) based on the formula the following were calculated.

Weight gain percentage:

(Initial body weight (g)-final body weight (g)/ initial body weight (g) ×100

Daily weight gain:

Average initial body weight (g)-average final body weight (g)/ average initial body weight (g) × (length of breeding period (days) ×100

Specific growth rate percentage

Logarithm of initial body weight (g)-logarithm of final body weight (g) / (length of breeding period (days) × 100

Feed conversion ratio:

Amount of consumed feed (g)/average dry body weight gain (g)

Protein efficiency coefficient:

The amount of eaten protein in the diet (g) / the amount of weight gain (g)

Total consumed feed:

Number of fish per tank/total weight of eaten feed

Fat efficiency ratio:

Fat consumed (g) / Weight obtained (g)

At the end of the design period, all fish will be starved for 48 h to empty the gastrointestinal tract, killed, and then weighed. Six of fish were randomly removed from each tank and autopsied.

Statistical analysis

Data were analyzed for the degree of variation and significance of difference based on the analysis of variance (ANOVA) to determine if significant differences (p < 0.05) existed between treatments.

Results of present study shown in Figs. 1–9 and Tables 1–2.

Average body weight gain

During the experimental period, the mean body weight gain for the control group was lower than the other experimental groups. The highest weight gain was observed in F treatment. The fish fed probiotics during the experimental period showed more weight gain than the control group, which indicates the positive effect of dietary supplements on the desired parameter (Fig. 1).

SGR (Specific Growth Rate)

During the experimental period, the mean daily body weight gain in the control group was lower than that shown in experimental treatments. The highest daily body weight gain was observed in F treatment. The lowest were obtained on the 15th and 30th days in the control group, on the 45th day in the B treatment and on the 60th day in the H treatment, which had no significant differences with each other. Added supplements had the ability to increase the amount of this parameter (Fig. 2). The slight significant difference between the treatments for increasing the body weight of the fish depended on the climatic conditions, species, age and environmental conditions of the fish.

Percentage of body weight gain

The percentage of body weight gain in the control group during the experimental period, except for treatment B on day 45 and treatments B and D on 60th day, was the lowest compared to the other experimental groups. On 15th and 30th day, the highest percentage of body weight gain belonged to treatment F and on 45th and 60th day, and the highest percentage belonged to treatment D (Fig. 3).

Specific growth rate percentage

According to the Fig. 4, it can be stated that the percentage of specific growth rate on the 15th day of the experiment in treatments A, B and control did not differ significantly, but with other treatments had a significant difference. On the 30th day of the experiment, no significant difference was observed between the control, B and E treatments, but there was a significant difference with treatments A, D, F and H. On 45th day of the experiment, the control group had the lowest percentage of specific growth rate compared to other treatments and this difference was significant. At the end of the experimental period, treatment D had the highest percentage of specific growth rate with a significant difference compared with other treatments. On the 15th day of the experiment, the lowest percentage of specific growth rate was reported for treatments A and D. The value of this index was higher than other treatments during the farming period compared with the control group.

Feed conversion efficiency

Feed conversion efficiency for treatments B, E and H on 60th day of the experiment was lower than the control group, but for other treatments in experimental periods the rate of this index was higher than the control group. According to the Fig. 5, feed conversion efficiencies increased in treatments containing probiotic with a concentration of 0.5% inulin and 10³ CFU/g compared to other treatments.

Feed conversion ratio

The ratio of feed conversion on 15th, 30th and 60th days in F treatment showed a significantly increase compared to other treatments, but on 45th day, the highest rate of this index was observed in treatment H. The feed conversion ratio of the diets fed with probiotics improved significantly during the farming period (Fig. 6).

Feed consumed

The amount of consumed feed by rainbow trout on the 15th day for the experimental groups did not show a significant difference. On 30th day of the experiment, the rate of this index in treatments increased significantly compared to the control group. This index on 45th day and 60th day in the control group was lower than other treatments, but it decreased with significant different (Fig. 7).

Protein efficiency coefficient

Protein efficiency coefficient in treatment B on 45th day and treatment H on 60th day for rainbow trout farming was lower than the control group but there was no significant difference. The rate of this index in other experimental treatments was higher than the control group, which in many cases had significantly differences. The highest level of protein efficiency coefficient was observed on 15th, 30th and 60th day of the experiments for the group F and on 45th day in the group containing 10³ CFU/g Bacillus (Fig. 8).

Fat efficiency ratio

The fat efficiency ratio on15th and 30th day of trout farming in the control sample was significantly lower than other treatments. The highest of fat efficiency ratio was observed on15th and 30th day for F treatment. On 45th and 60th day of the experiment, the fat efficiency ratio in treatment D was higher than other treatments (Fig. 9).

Tables 1: Growth and nutritional indices of rainbow trout during feeding and growth period

Storage time (Days)	Treatments	Average body weight gain	Daily weight gain	Specific growth rate percentage	Total feed consumed	Feed conversion coefficient
15th day	A	3.28 ± 0.30 b	0.34 ± 0.02bc	0.12 ± 0.01 a	16.92 ± 0.02 a	0.17 ± 0.02 b
	B	2.38 ± 0.42 a	0.31 ± 0.01 ab	0.13 ± 0.01 a	16.89 ± 0.11 a	0.16 ± 0.01 b
	D	3.64 ± 0.33 b	0.37 ± 0.02 cd	0.12 ± 0.01 a	16.84 ± 0.13 a	0.19 ± 0.01 bc
	E	4.35 ± 0.20 c	0.45 ± 0.04 e	0.21 ± 0.01 b	19.84 ± 0.09 a	0.23 ± 0.02 de
	F	4.48 ± 0.10 c	0.54 ± 0.02 f	0.20 ± 0.01 b	16.93 ± 0.05 a	0.25 ± 0.01 e
	H	3.36 ± 0.21 b	0.40 ± 0.01 d	0.20 ± 0.01 b	16.84 ± 0.14 a	0.21 ± 0.00 cd
	C	2.57 ± 0.27 a	0.27 ± 0.01a	0.13 ± 0.02 a	16.93 ± 0.05 a	0.14 ± 0.01 a
30th day	A	5.40 ± 0.34 c	0.62 ± 0.01 c	0.25 ± 0.02 b	17.82 ± 0.12 a	0.30 ± 0.01 b
	B	4.38 ± 0.41 b	0.54 ± 0.02 b	0.21 ± 0.01 a	17.85 ± 0.04 a	0.25 ± 0.02 a
	D	5.21 ± 0.29 c	0.62 ± 0.02 c	0.24 ± 0.01 b	18.11 ± 0.10 b	0.32 ± 0.02 b
	E	6.06 ± 0.23 d	0.62 ± 0.01 c	0.23 ± 0.02ab	18.31 ± 0.09 c	0.31 ± 0.02 b
	F	7.41 ± 0.14 e	0.82 ± 0.02 d	0.31 ± 0.01 c	18.41 ± 0.10 c	0.40 ± 0.01 c
	H	7.20 ± 0.07 e	0.79 ± 0.02 d	0.26 ± 0.0 b	18.13 ± 0.13 b	0.39 ± 0.01 c
	C	3.40 ± 0.34 a	0.43 ± 0.02 a	0.20 ± 0.01 a	17.69 ± 0.08 a	0.22 ± 0.02 a
45th day	A	8.56 ± 0.24 a	0.83 ± 0.02 a	0.40 ± 0.01 b	19.56 ± 0.06 c	0.43 ± 0.02 ab
	B	8.23 ± 0.23 a	0.82 ± 0.01 a	0.40 ± 0.01 b	19.35 ± 0.05 b	0.42 ± 0.01 ab
	D	9.26 ± 0.22 b	0.90 ± 0.01 bc	0.41 ± 0.01 b	19.68 ± 0.10 c	0.44 ± 0.02abc
	E	8.63 ± 0.22 a	0.85 ± 0.02 a	0.41 ± 0.01 b	19.67 ± 0.07 c	0.46 ± 0.01 c
	F	9.34 ± 0.23 b	0.92 ± 0.02 c	0.41 ± 0.01 b	20.56 ± 0.05 d	0.45 ± 0.02 bc
	H	9.31 ± 0.23 b	0.87 ± 0.01 ab	0.41 ± 0.02 b	20.25 ± 0.06 e	0.44 ± 0.01abc
	C	8.44 ± 0.30 a	0.84 ± 0.04 a	0.31 ± 0.01 a	18.89 ± 0.03 a	0.41 ± 0.01 a
60th day	A	14.44 ± 0.32d	1.25 ± 0.02 bc	0.44 ± 0.02 a	22.24 ± 0.06 c	0.63 ± 0.01 c
	B	13.46 ± 0.34ab	1.21 ± 0.01ab	0.45 ± 0.01 a	21.73 ± 0.05 b	0.58 ± 0.07abc
	D	14.27 ± 0.31cd	1.31 ± 0.01 d	0.51 ± 0.01 b	22.39 ± 0.09 c	0.64 ± 0.01 c
	E	13.74 ± 0.23ab	1.22 ± 0.03ab	0.45 ± 0.02 a	59.22 ± 0.17 d	0.56 ± 0.01 ab
	F	15.20 ± 0.16 e	1.29 ± 0.02 cd	0.45 ± 0.02 a	23.41 ± 0.12 e	0.62 ± 0.01 bc
	H	13.87 ± 0.21bc	1.20 ± 0.01 a	0.45 ± 0.0 0a	22.93 ± 0.06 f	0.55 ± 0.05 a
	C	14.44 ± 0.32 d	1.22 ± 0.02ab	0.44 ± 0.02 a	21.38 ± 0.10 a	0.63 ± 0.02 bc

The same letters in each column indicate that there is no significant difference (p < 0.05). “±number” was a standard deviation.

Tables 2: Survival, Status and nutritional indices of rainbow trout during feeding and growth period

Storage time (Days)	Treatments	Feed conversion ratio	Protein efficiency ratio	Fat efficiency ratio	Status index	Survival percentage
15th day	A	5.48 ± 0.21 e	0.40 ± 0.02 b	1.35 ± 0.02 b	1.57 ± 0.01 e	0.92 ± 0.00 a
	B	5.93 ± 0.07 f	0.37 ± 0.00 b	1.29 ± 0.01 b	1.25 ± 0.01 c	0.93 ± 0.01 ab
	D	5.13 ± 0.08 d	0.44 ± 0.01 c	1.51 ± 0.03 c	1.10 ± 0.01 b	0.95 ± 0.00 cd
	E	4.09 ± 0.07 b	0.55 ± 0.02 d	1.92 ± 0.05 e	1.04 ± 0.01 a	0.96 ± 0.01 d
	F	3.65 ± 0.11 a	0.60 ± 0.01 e	2.01 ± 0.02 f	1.07 ± 0.01 ab	0.95 ± 0.01 cd
	H	4.71 ± 0.11 c	0.48 ± 0.02 f	1.65 ± 0.06 d	1.07 ± 0.05 ab	0.940 ± .00 bc
	C	6.46 ± 0.23 g	0.32 ± 0.01 a	1.15 ± 0.02 a	1.37 ± 0.01 d	0.92 ± 0.00a
30th day	A	3.48 ± 0.22 b	0.70 ± 0.02 c	2.39 ± 0.19 c	1.41 ± 0.00 e	0.92 ± 0.01 a
	B	3.67 ± 0.14 c	0.61 ± 0.01 b	2.09 ± 0.0 b	1.13 ± 0.02 c	0.92 ± 0.01 a
	D	3.32 ± 0.09 b	0.68 ± 0.03 c	2.36 ± 0.05 c	1.16 ± 0.01 c	0.92 ± 0.01 c
	E	3.19 ± 0.15 b	0.74 ± 0.01 d	2.50 ± 0.14 c	1.03 ± 0.00 ab	0.96 ± 0.00 c
	F	2.45 ± 0.15 a	0.92 ± 0.0 0e	3.16 ± 0.08 d	1.06 ± 0.01 b	0.94 ± 0.01 b
	H	2.55 ± 0.06 a	0.91 ± 0.02 e	3.04 ± 0.04 d	1.02 ± 0.01 a	0.94 ± 0.01 b
	C	4.51 ± 0.29 d	0.47 ± 0.01 a	1.56 ± 0.17 a	1.33 ± 0.04 d	0.91 ± 0.00 a
45th day	A	2.42 ± 0.09 c	1.02 ± 0.01bc	3.46 ± 0.15 b	1.24 ± 0.01 c	0.92 ± 0.01 ab
	B	2.34 ± 0.05 bc	0.94 ± 0.01 a	3.18 ± 0.06 a	1.19 ± 0.01 b	0.92 ± 0.01 ab
	D	2.17 ± 0.04 a	1.05 ± 0.30 c	3.53 ± 0.16 b	1.03 ± 0.03a	0.95 ± 0.01 cd
	E	2.27 ± 0.06 abc	1.02 ± 0.02 bc	3.46 ± 0.05 b	1.03 ± 0.01a	0.96 ± 0.01 d
	F	2.29 ± 012 abc	1.03 ± 0.02 c	3.46 ± 0.13 b	1.04 ± 0.0a	0.97 ± 0.01 d
	H	2.23 ± 0.07ab	1.01 ± 0.02 bc	3.45 ± 0.10 b	1.02 ± 0.01a	0.94 ± 0.01 bc
	C	2.31 ± 0.05abc	0.98 ± 0.02 a	3.38 ± 0.03 bc	1.33 ± 0.01 d	0.91 ± 0.01 a
60th day	A	1.61 ± 0.09 ab	c 1.45 ± 0.02	4.89 ± 0.03 abc	1.36 ± 0.01 d	0.92 ± 0.01 ab
	B	1.66 ± 0.19 ab	1.39 ± 0.02 ab	4.69 ± 0.08 a	1.21 ± 0.01 c	0.92 ± 0.01 ab
	D	1.59 ± 0.81 ab	1.40 ± 0.02 bc	5.04 ± 0.05 c	1.16 ± 0.01 b	0.94 ± 0.01 bc
	E	1.56 ± 0.95 ab	1.41 ± 0.01 bc	4.48 ± 0.20 a	1.03 ± 0.01a	0.96 ± 0.01 d
	F	1.45 ± 0.08 a	1.47 ± 0.01 d	4.96 ± 0.07 bc	1.0 ± 0.02a	0.95 ± 0.01 cd
	H	1.71 ± 0.08 b	1.35 ± 0.02 a	4.75 ± 0.23 ab	1.0 ± 0.0a	0.96 ± 0. 00 d
	C	1.65 ± 0.07 ab	1.37 ± 0.04 a	4.70 ± 0.08 a	1.34 ± 0.01 d	0.90 ± 0.11 a

The same letters in each column indicate that there is no significant difference (p < 0.05). “±number” was a standard deviation.

In general, the results of the experiment showed that feeding fish with 1% dietary inulin as a prebiotic improves the fish's health far more than other treatments by increasing the immune response and blood biochemical parameters [40]. The present results showed that the consumption of inulin supplement at a low dose (2.5 g per kg of diet) at two levels of sorghum inclusion (15 and 30%) in the diet of Nile tilapia, increased the growth performance, immune-blood indicators, Parasitic infection and each of the liver and spleen structure of Nile tilapia fry. On the other hand, more studies are needed to definitively determine the effect of inulin supplementation to enhance immune responses and disease resistance in fish [41].

One of the most important issues in aquaculture production and breeding is proper nutrition management, because the use of good quality feed will improve growth rates and reduce production costs. Numerous studies have been conducted on the nutrition of rainbow trout, but there are still problems in the nutrition and breeding of this fish that need further research. Improving the feed situation will lead to greater profitability in the fish farming industry [29].

Baesi et al., [2] investigated the effect of probiotic lactobacilli on growth parameters and nutritional indices of common carp. His results showed that the specific growth rate, final weight, protein efficiency coefficient and fat efficiency ratio in the experimental treatment of 10⁶ CFU/g probiotic were higher than other treatments. Probiotic 10³ CFU/g treatment had the highest feed conversion efficiency and the lowest feed conversion ratio, but status index, liver index and visceral index did not show significant differences with the control group..

In a study by Yones et al., [37] the final weight, weight gain and specific growth rate of tilapia fed with the lowest inulin concentration were significantly different from the control group and other experimental groups. In addition, the feed conversion ratio, protein efficiency ratio, and pure protein intake of inulin-fed diets were improved during the rearing period. Consistent with this results, the results of the present study also showed that the average body weight gain, daily weight gain, feed conversion efficiency, protein efficiency coefficient, fat efficiency ratio and body weight gain percentage in samples supplemented with inulin was improved at lower concentrations than controls and samples containing higher concentrations of inulin. Contradictory results of inulin supplementation in fish nutrition were reported probably due to different levels of inulin dose, ferment ability by intestinal microbiome, and different intestinal morphology [10].

Based on the present study, treatments fed with diet containing Bacillus were significantly better than the control sample and compared to samples containing inulin in terms of growth performance and nutritional parameters. The study's results by Jafarian et al., [12], Ghobadi et al., [7] and Daniels et al., [3] were consistent with the results of this study. Increased growth and improvement of nutritional characteristics of fish fed diets containing probiotics due to increased appetite and secretion of enzymes or improved aquatic health as a result of infection control and increased digestibility [8]. Since bacteria can promote the production of vitamins and cofactors or by improving enzymatic activity [8], the presence of Bacillus probiotic supplement in the diet of salmon can be considered as positive factor in the experiment. Another similar study on the effect of probiotics on growth parameters by Wache et al., [34] showed that fish diets supplemented with probiotics improved fish diet and protein digestibility, which led to greater growth and better aquatic feed conversion ratio.

In several studies by Ghobadi et al., [7], Ferguson et al., [6] found that probiotic supplements added to the diet of carp and red tilapia resulted in 100% growth of fish. In the present study, experimental treatments fed with probiotics had a significantly higher growth rate than the control sample. One of the reasons for the high growth rate of fish fed with probiotics is the elimination of harmful bacteria in the fish digestive tract by beneficial probiotic bacteria. It is possible that the microbial flora in the gut, by secreting chemicals that have antimicrobial properties compared to other microbial communities, can affect the microbial population through competition for the absorption of available chemicals and energy [17]. Baesi et al., [2] also reported the positive effect of hyperbiotic Lactobacillus on growth, and nutritional parameters of common carp. His results showed that the specific growth rate, final weight, protein efficiency coefficient and fat efficiency ratio in the experimental treatment of 10⁶ CFU/g probiotic were higher than other treatments. The 10³ CFU/g probiotic treatment had the highest and feed conversion efficiency and the lowest feed conversion ratio. The results of this study also showed a positive effect of Bacillus on growth performance and nutritional indices of rainbow trout during the rearing period, so that in many cases with the control group, there was a significant difference.

Some possible methods of probiotic activity include competitive exclusion. In other words, probiotics inhibit potential pathogens in the gastrointestinal tract by producing inhibitory compounds or by competing for nutrients or space and modifying microbial metabolism. In addition, probiotics can stimulate host immune responses and vitamin production, detoxify dietary compounds, or break down indigestible compounds, which in turn can improve nutrition and stimulation [11]. However, exogenous enzymes produced by probiotics have a small maximum contribution to the total enzymatic activity of the intestine, and the presence of probiotics may stimulate the production of endogenous enzymes by fish [36]. Increased enzymatic activity with diets containing probiotics improves the digestion of protein, starch, fat, and cellulose, which in turn may explain the better growth observed with probiotic supplement diets. Tilapia larvae increase growth rate and feed conversion for 9 weeks [15]. According to a study, the use of the commercial species Bacillus spp. On rainbow trout during the first two months of feeding led to a significant growth (p < 0.05) in the treatment groups compared to the control group. Also, specific growth rate, feed conversion ratio and protein yield ratio improved significantly in the probiotic groups compared to the control group [1]. In a similar experiment on catfish by Queiroz and Boyd, [23], it was reported that a commercial bacterial mixture was prepared from Bacillus spp., which, mixed with breeding water, increased the growth of catfish (Ictalurus punctatus). The mixtures of Bacillus subtilis and Bacillus licheniformis added to the diet of rainbow trout (Oncorhynchus mykiss) after feeding on complementary diets for 10 weeks, significant improvement in feed conversion ratio (FCR), specific growth rate (SGR) and ratio Showed protein efficiency (PER) [21]. The results of the present study also clearly showed the beneficial effects of probiotics prescribed through nutrition on the growth rate of rainbow trout (Oncorhynchus mykiss). According to the results of the present study, the use of Bacillus, especially at a concentration of CFU/g 10³ in rainbow trout (Oncorhynchus mykiss) led to a significant increase in weight and growth of experimental groups at the end of the feeding period.

In the present study, growth parameters such as mean body weight gain, daily weight gain and body weight gain percentage, nutritional parameters such as feed conversion ratio, fat efficiency ratio, protein efficiency ratio, fat efficiency ratio as well as percentage fish fed a diet containing probiotic were significantly improved compared to the control group (Tables 1–2). Adding probiotics to diets improved growth performance, feed intake, and digestive enzyme activity. Improving the enzymatic activity obtained with supplemental diets shows that the addition of probiotics improves the digestibility of feed, including proteins, starches, and fats [35]. Sun et al., [31] and Soleimani et al., [30] stated that the combination of Enterococcus faecium probiotic and fructoolposaccharide as probiotic led to increased fish growth performance. In the study of Talebi Haghighi et al., [32], the effect of different concentrations of probiotic on the growth rate of whitefish was studied. Growth percentage was highest in all experimental treatments, which is consistent with the results of this study. In another study conducted by Mehrabi et al., [20], an increase in growth parameters of rainbow trout juveniles fed with probiotic supplement was observed compared to the control treatment. In research by Dehaghani et al., [4] stated that the probiotic used in common carp diet could significantly increase weight gain, length gain, specific growth rate and weight gain percentage, but had no significant effect on fish growth. The different levels of synbiotic have the ability to increase probiotic replacement and improve the activity of digestive enzymes, which leads to improved gastrointestinal function and ultimately increased growth [13]. These enhanced protease activities may be useful for the digestion of dietary protein, which in turn may contribute to better feed utilization in normal carp juveniles [38] and the strengthening of probiotics by addition of prebiotics, in addition, bacteria have been able to increase the production of vitamins and cofactors by improving the activity of enzymes [8].

According to Bagheri et al. [1], over time and with increasing duration of probiotic supplements, the density of probiotic bacteria in the intestine and its contents increases. In fact, if probiotic supplements are regularly present in the fish diet and given to the fish, it can change the dominant colony in the intestine and by removing the desired bacteria from the diet, the amount of bacteria in the gut shrinks rapidly. In the present study, the results showed that over time, the effect of the used supplements increased, which is probably due to increased density of bacteria in the intestine.

To summarize, a synbiotic is a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host. Two categories of synbiotics are recognized. A complementary synbiotic is composed of a probiotic and a prebiotic that together confer one or more health benefits but do not require co-dependent function; the components must be used at doses that have been shown to be effective for the components alone. A synergistic synbiotic contains a substrate that is selectively utilized by the co-administered live microorganism(s). Synbiotic products are not confined to human applications but could also include companion animals and livestock [14].

The results obtained at the end of the 60th day feeding rainbow trout (Oncorhynchus mykiss) with diets supplemented with a synbiotic (inulin + Bacillus) showed that the growth and nutrition indices in the treatments comparing to the group the control was significantly improved. The probiotic added to the diet had a better condition in terms of the mentioned parameters than the control. In fact, the simultaneous use of inulin and Bacillus can have better performance than use of supplements. The results showed that the level of 0.5% inulin and CFU/g 10³ Bacillus was the most desirable experimental treatment, so this concentration of probiotic in the diet increased growth rate and improved the fish nutritional indices.

Conflicts of Interest

Authors declare no conflicts of interest.

Data availability

The datasets analyzed during the current study are available from the corresponding author on reasonable request.

Acknowledgement

The authors are grateful to The Behbahan Khatam Alanbia University of Technology, Behbahan, Iran, for providing necessary facilities and financial support needed for carrying out the research.

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No competing interests reported.

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Nutrition and growth of rainbow trout (Oncorhynchus mykiss) fed diets supplemented with a synbiotic preparation

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Abstract

Figures

Introduction

Materials And Methods

Preparation of experimental treatments

Preparation of fish feed

Statistical analysis

Results

Average body weight gain

SGR (Specific Growth Rate)

Percentage of body weight gain

Specific growth rate percentage

Feed conversion efficiency

Feed conversion ratio

Feed consumed

Protein efficiency coefficient

Fat efficiency ratio

Discussion

Conclusions

Declarations

References

Additional Declarations

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